DE4137778A1 - Small solid fuel combustion unit control - involving electric heating of afterburner controlled in accordance with outlet gas temp. and oxygen content measurements. - Google Patents

Abstract

The method involves burning fuel, partic. solid fuel, in a combustion chamber (41). The combustion chamber is combined with an afterburner (42) to which sec. air is supplied through a flap (63) linked (65) to a control unit (59). The afterburner is heated by electric elements (51) in five separate sections (52-56) of the wall, selected (58) in accordance with the temp. and/or free oxygen concn. of the hot gas, measured by sensors (66,67) in the outlet to a waste-heat boiler (40) in the chimney. USE/ADVANTAGE - For e.g. domestic wood-burning stoves, emissions are reduced in all conditions of load or fuel quality, without high electric current consumption.

Description

The invention relates to a method for operating egg ner combustion device, in particular for solid burning substances in which the fuel passes through in a firing chamber Heat decomposes with the release of flammable gases that is in a preset temperature range controlled by means of electrically heated afterburning chamber supplied air are oxidized.

This procedure with electric heating the night combustion chamber is known (DE 31 12 976 A1). There will be solid fuels such as wood in heating stoves for building heating or burned in open fireplaces or tiled stoves, whereby all of the combustion air into the combustion chamber Firing chamber enters and that into the post-combustion chamber flowing flue gas already provides the post-combustion air required carries along. The chimney draft determines the start of combustion air whose throughput is not regulated. For afterburning the in the combustion chamber by appropriate heating from the Gases escaping but only partially burned in the post-combustion chamber through which the flue gases flow an electrically heated glow grille arranged with thermo static control is heated to approx. 1070 ° K. Independently of the various operating states that are present in the Anhei zen, with partial fire (partial load), with full fire (full load), with  Burning out and resulting in breaks in combustion, the incandescent grid constantly heated to the aforementioned temperature or in the appropriate temperature range, what with a high Power consumption is connected. The elek electrical energy to the useful heat of the furnace, the electrical However, heat generation is generally expensive and is one oven specifically designed for combustion badly used.

Otherwise, the electric heating is afterburning chamber to ensure compliance with the requirements for a complete Burnout required minimum temperature a suitable means environmental pollution caused by incinerators put. In this regard, the house fire represents a significant one Emission source. There are often simple fires here systems with low output (up to approx. 25 kW heating output) despite loading with good and low emissions thermal usable fuels to visible and invisible air pollution which are considerable in sum.

When using suitable fuels, the combustion is in the white depends largely on the following four parameters: temperature, the dwell time of the flammable substances in one sufficiently high temperature range, the supply of oxygen and the mixture or turbulence of combustion air and Ver combustion gases. The combustion process, in particular especially for solid fuels such as B. wood, simplified in Divide the following four sub-processes: drying, decomposition of the fuel in gases and carbon (pyrolysis), implementation of the carbon in gaseous state and oxidation of the flammable gases. Relevant studies and findings are designed in modern combustion plants by the design of the Fuel rooms and the afterburning zones as well as by the Use of complex regulations and not least by the Ver Use of support burners to maintain the minimum temperature ren considered.

Even in low-power incinerators for heating and Hot water generation in detached houses and small residential complexes enormously improved incinerators are already offered, which in the nominal load range is largely complete and therefore cause low-emission combustion. During the heating process and while  However, the burning behavior remains as it is during the burnout phase unsatisfactory, which is often due to smoking chimneys and there with associated odor nuisance to the outside occurs. Especially for small furnaces under 25 kW, for which the Invention is primarily intended, and in particular at those without automatic loading often come to heating and burnout with very different operating conditions. This is where the well-known electrical heating of the Nachver works combustion chamber by means of the glow grille positive because too at least one parameter for good low-emission combustion, namely the maintenance of a minimum temperature is.

The invention has for its object the combustion to improve so that the emissions not only at nominal load but in all load ranges or with all different which operating states of the combustion device and also be reduced with different fuel properties, without this result requiring high power consumption.

This task is described in connection with the above electrical heating of the post-combustion chamber fiction moderately solved in that the post-combustion air directly into the Afterburning chamber initiated and their throughput depend the temperature and / or the free oxygen content of the afterburned hot gas is regulated.

In a corresponding manner, the invention also relates to a ver Combustion device with one that can be charged with the fuel Brenngutkammer, an electrically heated afterburning chamber and an air supply (DE 31 12 976 A1), which he according to the invention characterized in that in the afterburning chamber a line with a control flap for afterburning air opens and that a control unit is provided, which Signal lines with at the output or behind the afterburning chamber arranged, influenced by the hot gas sensors for the temperature and / or the free oxygen content and with the Electric heating of the chamber associated with the afterburning chamber temperature sensors and control lines with the rule flap and the electric heater is connected.  

Appropriate refinements and developments of the method and the combustion device according to the invention itself from the subclaims.

The invention is based on the knowledge that in a good Combustion device alone during nominal load operation by burning a temperature in the post-combustion zone is reached and can be kept, the one in the we substantial complete afterburning guaranteed, so that an additional electrical heater is then unnecessary. Further lies considering that during heating and burning out In comparison to the nominal load operation a smaller amount of flammable and combustible gases, possibly also parti from which fuel is released, making it possible during these critical phases regarding emissions reduce the amount of air passed through the oven so that no cooling caused by unnecessary excess air electrically heated internals occurs and a related hanging demand for electrical energy is avoided. Ent speaking of the then reduced amount of air caused by the burning flows well, the risk is reduced that particles with be torn and remain unburned. Otherwise, one would uselessly high excess air also the firing engineering reduce degree of efficiency.

The previously unknown electrical heating also the burner gutkammer, in which the heating (possibly also drying) and Zer Settling or gasification of the fuel must be special expedient. The fuel then no longer has to be manually or ignited in some other way, rather it heats up as a result the electrical heating up to a temperature at which the inflammation as a result of sufficient oxygen supply occurs.

It is even possible to have no or only the firing chamber little air to supply that there is little or no air here Combustion takes place. The heating of the fuel is too ner gasification is then more or less completely by the Electric heating causes. Such a burning process process is characterized by an extremely low dust emission off, since only water vapor (if the Fuel is damp) and the flammable gases are exceeded. The  in the case of a partial incineration the firing chamber - depending on the fuel and the flow speed of the fuel entering the afterburning zone Flue gas - dust particles in the afterburning zone wear. These dust particles are at least partially removed from the Gases flowing to the chimney are entrained heat exchangers and at least partially leave the chimney into the ambient air, provided there are no devices for restraint or separation are provided. A low air intake to the firing chamber is necessary when out of the firing Substance created by the decomposition of carbon in the Brenngutkammer must be oxidized to carbon monoxide, which then burned to carbon dioxide in the afterburning chamber becomes.

In the post-combustion chamber, the electrically heated Internals already in the start-up phase of the combustion process, while little flammable gases are released, whose Combustion to its own sufficient heat development a largely complete oxidation is not yet sufficient Gases from the fuel and also lead to a Ver vaporization and subsequent combustion of possibly from the burner released particles that otherwise z. B. in the form of Aerosols the so-called "blue smoke" at the Holzver form a burn.

The conditions described above for the heating phase apply mutatis mutandis to the termination of the pre-combustion gangs, because then for a good burnout of the burn gases required temperature due to insufficient fuel required or too little gas quantity due to the burning the electrical process itself can be maintained heating but also in this case the required or missing Provides thermal energy.

By evaluating the outlet temperature and the free Oxygen content in the afterburned hot gas (before it cools down heat extraction for space heating, hot water generation or other use) can be the combustion device air supply and / or air distribution in the sense of regulate the aforementioned invention task. This can happen so that with sufficient hot gas temperatures and with uselessly high  Excess air the air supply into the afterburning chamber is throttled and / or the air supply to the firing chamber is increased in order to start the combustion and so that for one complete afterburning required high temperatures to maintain or maintain the combustion process and so the combustion process in an advantageous lei area of responsibility.

An additional electric heater also for the firing chamber is there involved in the regulation to such an extent that with start-up Combustion process this heating power is reduced to elek save energy and an excessively fast Zer to avoid fuel setting, which would result in this could result in insufficient combustion air can be supplied. Corresponding retailers often work combustion plants with natural draft and associated with additional Chen fluctuations in the chimney draft, which then have an influence of the air flow. Would also approve Large amounts of air pose the risk that they are full for you constant burnout required dwell time of the combustion gases in a high temperature range.

The solid fuels with which combustion devices and small combustion plants in particular are frequently loaded different properties that the combustion be to meet. Add to that the release of flammable gases the fuel depends on the temperature, which of the Is exposed to fuel. A simple consideration of that conditions and adaptation to the mostly fluctuations The decrease in heat is thereby within the scope of the invention achieved that the decomposition of the fuel over the in the Combustion material chamber and / or over the in the Controlled electrical heating output brought into the firing room becomes.

It is readily understandable to the person skilled in the art that with one suitable control system the electrical heating at least the Afterburning chamber after heating up and reaching the Minimum temperature of the exiting the combustion chamber Hot gas, the electric heating also fluctuates greatly Load ranges are significantly restricted or even entirely can be omitted and only take place again in the burnout phase  must, with downtimes or combustion breaks with a minimal use of electrical energy can be bridged can. By using microprocessors, the Combustion process in terms of energy consumption, the Efficiency and ease of use, but especially also regulate advantageously with regard to emissions behavior.

If the combustion device according to the invention by a automatic loading, which is conveniently supplemented by the heat demand should be controlled, so can not only the ease of use but also the emission behavior improve further. The otherwise with solids renewals, in particular other wood firing systems, for good thermal efficiency and low emissions recommended buffer storage can general omitted, especially if one is sufficient proper heat is secured without the behavior the existing disadvantages shows current effects. This reduces the space investment costs may and may decrease. The planned monitoring However, control, regulation and electrical heating do that Connection to a power source required.

The electric radiators can be advantageously in the feu discovered lining or into the walls of the afterburning mer and possibly integrate the Brenngutkammer, so that they before corrosive influence of the flue gases are protected. The warmth a green supports the capacity of the heated wall surfaces constant control behavior. Also the associated temperature sensors can be accommodated in the wall surfaces. Furthermore, it is advantageous if these wall surfaces as easily replaceable Components are formed.

In summary, it can be said that a fiction according to the combustion carried out even with low heating outputs Extremely low emissions over large load ranges, without visible ones Smoke and very economical takes place without the burning material or the operation of the system are put. The respective Operating status can be made visible, and it can from the Control issued appropriate instructions for operation will.

Three embodiments of the invention are set out below explained in more detail by means of a schematic drawing:

Fig. 1 shows a combustion device with electrical heating of the post-combustion chamber and regulated air supply to the respective mer Brenngutkammer and Nachverbrennungskam;

Fig. 2 is a combustion device in which both the combustion chamber as well as the post-combustion chamber are each electrically heated and provided with an adjustable air supply; and

Fig. 3 shows a combustion device with automatic loading, in which both the combustion chamber and the after-combustion chamber are heated, but combustion air is only supplied to the after-combustion chamber.

The combustion apparatus of FIG. 1 comprises a combustion material chamber 1 and then to this a post-2, which jacket-shaped within a common Isolie tion 3 are arranged. A loading door 4 at the entrance to the firing chamber 1 enables the fuel to be introduced. As such, primarily wood or a wood-containing fuel is provided. However, other solid and - with appropriate design of the combustion device - liquid fuels are also possible.

The afterburning chamber 2 has interchangeable components designed chamber walls 5 , 6 and 7 , in each of which a plurality of electric radiators 8 are installed. The radiators of each chamber wall are combined to form a radiator group 9 or 10 or 11 with its own heating circuit, so that three independent heating circuits are available.

At the post-combustion chamber 2 is followed by a transition zone 12 through which the hot combustion gases are supplied for heat use. For this purpose, a pipe 14 through which a heat transfer medium flows is arranged within a heat exchanger jacket 13 . Here, the useful heat is extracted from the hot gases flowing to the chimney 15 .

For the supply of the combustion air, a Gesamtluftlei device 16 is provided with a control flap 17 , to which a combustion air line 19 opening into the combustion chamber 1 and a line 20 opening into the post-combustion chamber 2 for post-combustion air are connected to a control distributor flap 18 . In the post-combustion chamber 2 , the sensor 21 of a temperature measuring device 22 and the sensor 23 of a measuring device 24 for the free oxygen content in the after-burned hot gas are also arranged on the output side. The sensors 21 and 23 are still shown in Fig. 1 in the area of the afterburning chamber, but they are preferably at the very end of the afterburning chamber 2 and possibly already in the transition zone 12 net.

The combustion device shown is assigned a Steuerein unit 25 , which is connected to the mains via a power line 26 and receives the current data on the temperature and the oxygen content of the escaping hot gas from the measuring devices 22 and 24 via signal lines 27 and 28 . Furthermore, the control unit 25 receives information about the respective temperatures of the chamber walls 5 , 6 and 7 via indicated heating circuit signal lines 29 , 30 , 31 , for which purpose chamber temperature sensors (not shown) are installed, with which the heating circuit signal lines 29 , 30 , 31 are connected.

In a similar manner, three heating circuit control lines 32 , 33 , 34 are connected to the control unit 25 , which (not shown) lead to the three radiator groups 9, 10 and 11 , respectively, and determine their heat output. Furthermore, from the control unit 25 control lines 35 and 36 , via which the position of the control flap 17 and the control distributor flap 18 and thus the supply of the combustion air into the combustion chamber 1 and the post-combustion air into the post-combustion chamber 2 can be influenced in the desired manner.

Since it has already been explained in the preceding description how the combustion device is to be driven or regulated in adaptation to the respective circumstances, in particular the different operating states when heating up, in part-load operation, in full-load operation, when burning out and during combustion breaks, this can be dispensed with here to describe all situations that occur and the tax consequences that arise. However, it should be emphasized that generally a complete post-combustion of all combustible gases is achieved by the fact that the chamber walls 5 , 6 , 7 are brought and held to high temperatures in the range of 1000 ° K - depending on the circumstances, more or less initially only by electrical heating and then less or more by the heat of combustion. Accordingly, the Nachver combustion chamber 2 is heated up at least before and during the heating phase and normally also at partial load by means of the three heating circuits or heating element groups 9 , 10 and 11 , while in full-load operation electrical heating can be largely or completely dispensed with because the heat development by Combustion process (heat of combustion) already ensures sufficient temperatures in the afterburning chamber 2 or in the exhaust air stream emerging therefrom, which goes into the control via the heating circuit signal lines 29 , 30 and 31 and thus leads to a reduction in the consumption of electrical energy.

Another important aspect is that always works with an air supply adapted to the respective operating state and an unnecessary excess of air is avoided, for which purpose the respective content of free oxygen in the burned hot gases via the signal line 28 is entered into the control system. The air supply can also be used in such a way to ensure complete afterburning that, for example, the supply of combustion air to the combustible chamber 1 is practically completely prevented in the heating phase and the combustion process is thereby delayed until the chamber walls 5 , 6 and 7 so are heated up to the point that a complete combustion or afterburning of the gases released from the firing material and thus an emission of exhaust air through the chimney 15 to the environment which is optimized with regard to the content of unburned ingredients is ensured.

A person skilled in the art knows how a corresponding control system can be equipped with modern microprocessor technology and operated on the basis of input individual input data. It can be very useful to combine an operating display with the control unit 25 , which gives status data and operating instructions for additional manual operation, in this combustion device in particular with regard to the manual loading of fuel.

The combustion device according to FIG. 2 corresponds in many ways to the system already described with reference to FIG. 1. It is equipped with a waste heat boiler 40 and has a Brenngutkam mer 41 and a post-combustion chamber 42 within an insulation 43 . In addition to a loading door 44 to the combustion material chamber and an access door 45 is provided to the post-combustion chamber 42nd Deviating from the embodiment according to FIG. 1, the Brenngutkammer 41 is electrically heated. Accordingly, five groups of radiators 46 to 50 with electrical Heizkör cores 51 in five formed as separate components chamber walls 52 to 56 are arranged. The five radiator groups 46 to 50 are fünfinsgesamt obligations with 57 designated heating circuit Signallei and fünfinsgesamt 58 designated lines are associated with the heating circuit control. These are only shown in the area adjacent to the control unit 59 . The division into five heating circuits enables independent electrical heating of the two chambers 41 and 42 and, moreover, also a locally differentiated supply of the electrical thermal energy, which is adapted to the circumstances.

In the combustion chamber 41 , a combustion air line 60 opens with a control flap 61 , while in the afterburning chamber 42 a line 62 opens with a control flap 63 for afterburning air. So here completely separate air lines 60 and 62 are provided, the control flaps 61 and 63 via control lines 64 and 65 are provided by the control unit 59 ver.

Here, too, two sensors are arranged in the hot gas stream or behind the afterburning chamber, which advises the temperature and free oxygen values to the Temperaturmeßge 66 or to the measuring device 67 for the oxygen content. The sensors are arranged in the transition area of the hot gas to the waste heat boiler 40 . The corresponding values are transmitted to the control unit 59 via the signal lines 68 and 69 .

The combustion device according to FIG. 3 corresponds in some respects to the embodiment according to FIG. 2. In this case, a waste heat boiler or another intended use of heat has been omitted. The main difference is that an automatic loading of fuel is provided and there is no possibility of supplying combustion air into the combustion chamber.

Referring to FIG. 3, both the Brenngutkammer 71 as the post combustion chamber 72 heated electrically, including components designed as chamber walls are provided with electric heaters 73 to 78 and 79 accordingly radiator groups 80 to 85. The heating circuit signal lines 87 connected to the control unit 86 and the heating circuit control lines 88 are assigned to these.

Are connected to the control unit 86 as in Figs. 1 and 2, the power line 26 and a signal line 89 connected to the control unit 86 notifies the respective heat demand. In the same way as in FIG. 2, the control unit 86 receives information about the temperature and the free oxygen content in the hot gas leaving the afterburning chamber 72 via the signal lines 68 and 69 .

Before the fuel chamber 71 are a filler opening ver closed by a cover 90 for the fuel and a cal matically indicated charging device 92 with a drive motor 93 are provided, which is controlled via a control line 94 by the control unit 86 .

Combustion air is only introduced into the after-combustion chamber 72 via the line 95 - depending on the position of the control flap 96 , which is adjusted via the control line 97 by the control unit 86 . The display line 98 also emanating from the control unit 86 can be led to the heat consumer in order to provide feedback on the heat demand through the signal line 89 and or to display operating status data of the combustion device.

The combustion apparatus according to Fig. 3 operates particularly in emissions because the thermal energy for degassing or Pyroly Sieren of the fuel is generated only electrically in Brenngutkammer 71, the firing material is thus not flowed through by combustion air, which would promote entrainment of particles from the combustion material.

Combustion devices, as shown by way of example in FIGS. 1, 2 and 3, can be equipped with automatic ash removal devices and can thus be designed for uninterrupted operation even over long periods of time. The control unit can be used in conjunction with the measuring device for the outlet temperature of the exhaust air from the combustion device to ensure that an upper temperature limit is not exceeded for fuels with a high calorific value, so as to avoid the formation of thermal nitrogen oxides.

The combustion according to the invention works particularly advantageously device with a specially in the form and / or burning nung properties matched fuel, such. B. dried Wood, pressed wood (e.g. from largely dried wood chips pressed cubes or briquettes) or a fuel mixture, such as e.g. B. a compressed mixture of dried wood chips and Carbon particles that a feeder particularly is fit.

Claims (18)

1. A method of operating a combustion device, in particular for solid fuels, in which the fuel in a combustible chamber ( 1 , 41 , 71 ) is decomposed by the action of heat under the release of combustible gases, which are electrically heated in a preset temperature range post-combustion chamber (2, 42, 72) is oxidized by means of air supplied, are characterized in that the post-combustion air introduced directly into the Nachverbren drying chamber (2, 42, 72) and their throughput as a function of the temperature and / or the free oxygen content of the afterburned Hot gas is regulated. 2. The method according to claim 1, in which the combustion air is introduced directly into the firing chamber ( 1. 41 , 71 ), characterized in that the throughput of combustion air is regulated in dependence on the temperature and / or the free oxygen content of the afterburned hot gas becomes. 3. The method according to claim 1 or 2, characterized in that the firing chamber ( 1 , 41 , 71 ) is controlled electrically heated in a preset temperature range. 4. The method according to claim 3, characterized in that the fuel is decomposed by electrical heating of the firing chamber ( 1 , 41 , 71 ) while releasing gas. 5. The method according to claim 3 or 4, characterized in that the firing chamber ( 1 , 41 , 71 ) is only electrically heated when the post-combustion chamber ( 2 , 41 , 72 ) be already heated to the nominal temperature or a predetermined minimum temperature is. 6. The method according to any one of claims 1 to 5, characterized in that during combustion breaks the electrical cal heating of the post-combustion chamber ( 2 , 42 , 72 ) and / or possibly the combustible chamber ( 1 , 41 , 71 ) redu according to a lower preset temperature range is decorated. 7. The method according to any one of claims 1 to 5, characterized in that the electrical heating of the afterburning chamber ( 2 , 42 , 72 ) and / or possibly the combustible material chamber ( 1 , 41 , 71 ) is completely switched off with a wake when combustion breaks begin . 8. The method according to any one of claims 1 to 7, characterized in that the combustible chamber ( 1 , 41 , 71 ) in accordance with the heat requirements and / or a predetermined heat output is regulated with the fuel is charged. 9. The method according to any one of claims 1 to 8, characterized in that the post-combustion chamber ( 2 , 42 , 72 ) and / or the firing chamber ( 1 , 41 , 71 ) supplied air is preheated, in particular with waste heat from the combustion device. 10. Combustion device for performing the method according to claims 1 to 9, with a combustible with the combustible combustible chamber ( 1 , 41 , 71 ), an electrically heatable afterburning chamber ( 2 , 42 , 72 ) and an air supply guide, characterized in that in the afterburning chamber ( 2 , 42 , 72 ) a line ( 20 , 62 , 95 ) for after combustion air with a control valve ( 17 , 63 , 96 ) opens and that a control unit ( 25 , 59 , 86 ) is provided, which Signal lines ( 27 , 28 ; 68 , 69 ) with at the output or behind the afterburning chamber ( 2 , 42 , 72 ) arranged, hot gas-influenced sensors ( 21 , 23 ) for the temperature and / or the free oxygen content and via heating circuit - Signal lines with the electrical heating ( 9 , 10 , 11 ; 48 , 49 , 50 ; 83 , 84 , 85 ) of the post-combustion chamber ( 2 , 42 , 72 ) assigned to chamber temperature sensors as well as control lines ( 35 , 65 , 97 ) with the control flap ( 17 , 63 , 96 ) and via heating circuit control lines ( 32 , 33 , 34 ; 58 ; 88 ) with the electric heater ( 9 , 10 , 11 ; 48 , 49 , 50 ; 83 , 84 , 85 ) is connected. 11. Combustion device according to claim 10, characterized in that in the combustible material chamber ( 1 , 41 ) a combustion air line ( 19 , 60 ) with a control flap ( 18 , 61 ) opens out via a control line ( 36 , 64 ) with the control unit ( 25 , 59 ) is connected. 12. Combustion device according to claim 11, characterized in that a control flap ( 17 ) for the supply of the total air and a control distributor flap ( 18 ) for the distribution of the total air to the firing chamber ( 1 ) and the post-combustion chamber ( 2 ) are provided. 13. Combustion device according to one of claims 10 to 12, characterized in that the combustion chamber ( 41 , 71 ) with an electric heater ( 46 , 47 , 48 ; 80 , 81 , 82 ) is seen ver, which via a control line ( 58 , 88 ) is controlled by the control unit ( 59 , 86 ). 14. Combustion device according to one of claims 10 to 13, characterized in that the radiators ( 8 , 51 , 79 ) of the electric heater ( 9, 10 11; 46 to 50; 80 to 85 ) into the chamber walls ( 5 , 6 , 7 ; 52 to 56 ; 73 to 78 ) are integrated. 15. Combustion device according to claim 14, characterized in that the chamber temperature sensors are integrated into the chamber walls ( 5 , 6 , 7 ; 52 to 56 ; 73 to 78 ). 16. Combustion device according to claim 14 or 15, characterized in that the chamber walls ( 5 , 6 , 7 ; 52 to 56 ; 73 to 78 ) with the integrated radiators ( 8 , 51 , 79 ) and optionally integrated chamber temperature sensors are replaceable components. 17. Combustion device according to one of claims 10 to 16, characterized in that the firing chamber ( 71 ) is assigned a loading device ( 92 ) with a drive ( 93 ) which is connected via a control line ( 94 ) to the control unit ( 86 ) . 18. Combustion device according to one of claims 10 to 17, characterized in that it has an automatic Ash removal device is equipped.